The present invention relates to fasteners and, more particularly, to a guidance and retention member for use with a nail-like fastener to be driven by a powder-actuated tool.
When driving nail-like fasteners by means of a powder-actuated tool, it is common practice to utilize a tip member, disposed on the forward or nose end of the fastener, to center and hold the fastener in the tool muzzle bushing prior to setting. One such tip member comprises a hollow, elongate, cylindrical body having a number of flexible, congruent, radially extending fins integrally formed thereon.
Tip members of this general type are presently used extensively in the application described. Such tip members have, however, been found to suffer in that, as the interference of the circumscribed diameter formed by the fins increases relative to the muzzle bushing bore diameter, asymmetric deflection of the fins may occur. This asymmetry causes a degree of eccentricity between the fastener and the driving piston which results in the fastener entering the target at an angle, yielding a poor fastening or even a broken fastener. If the thickness of the individual fins is increased to minimize the deflection thereof, the force required to insert the tip member into the bushing bore is greatly increased, making it undesirable for use in smaller sized tool bores. On the other hand, if the thickness of the individual fins is decreased to accomodate insertion in small bores, then in larger bores, the tip member will be too flexible to provide the necessary support for proper fastener guidance. Further, due to the nature of the elastomeric materials commonly used for tip members, the problem of insertion is significantly increased as the ambient temperature decreases and material stiffness increases.
It is, therefore, a primary object of the present invention to provide a fastener tip member which will offer proper fastener guidance in a range of sizes of muzzle bushing bores, while reducing the force required for insertion of the tip member into the said bore. This is accomplished, in general, by the provision of two sets of fins, the fins of one set being of substantially greater length, or radial extent, than the ones of the other. More specifically, the fins of the shorter set are 40-60% the length of those of the longer set; the fins of both sets being disposed in alternating relation about the outer cylindrical surface of the tip member body. The shorter fins, although nominally of the same thickness as the longer fins, are more rigid by virtue of their lower length-to-thickness ratio. Hence, they act to prevent the fastener point from being deflected off-center of the bushing bore by more than half the difference between the bore diameter and the circumscribed diameter defined by the said shorter fins.